1. Technical Field
The disclosure relates generally to an electric vehicle and a control method for an electric vehicle, and relates more specifically to a control technique of inhibiting deterioration of a secondary battery mounted in an electric vehicle.
2. Description of Related Art
As a secondary battery is charged with electricity or electricity is discharged from the secondary battery, the salt concentration in an electrolytic solution of the secondary battery becomes non-uniform, resulting in an increase in the internal resistance of the secondary battery. Such an increase in the internal resistance due to a non-uniform salt concentration may be caused especially by high-current charging or high-current discharging. Deterioration of the secondary battery thus caused is referred to as, for example, “high-rate deterioration”, in distinction from aged deterioration.
According to Japanese Patent Application Publication No. 2010-60406 (JP 2010-60406 A), when an evaluation value that may indicate the degree of high-rate deterioration exceeds a prescribed value, the control central value of state of charge (SOC) that indicates the remaining capacity of the secondary battery is adjusted (changed). Specifically, a monitoring device described in JP 2010-60406 A lowers the control central value of the SOC to a value below a normally set value, thereby allowing the secondary battery to be charged with a larger amount of electricity. As a result, the battery resistance is promptly recovered to a normal state.
However, when the control central value of the SOC is lowered to a value below the normally set value, the secondary battery is used in a low-SOC range (range in which the SOC is low). In the low-SOC range, expansion and contraction of the negative electrode of the battery become large and thus an electrolytic solution in a battery cell is more easily pushed out. Thus, the salt concentration in a battery cell surface more easily becomes non-uniform. As a result, “high-rate deterioration” described above may be promoted.